Polymerization of cyclic olefins

ABSTRACT

A catalyst and process for the polymerization of cyclic olefins, such as dicyclopentadiene, are disclosed. The catalyst includes a transition metal compound and a borohydride co-catalyst, with optional boron halide promoter. Polymerization can be carried out in a reaction injection molding process to prepare a thermoset molded article.

This is a continuation of application Ser. No. 331,560, filed Mar. 31,1989 and now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to the polymerization of cyclic olefins. In oneembodiment, the invention relates to a catalyst for the reactioninjection molding of dicyclopentadiene.

Cyclic olefins are subject to ring-opening metathesis polymerization toproduce thermoset polymers having physical properties making themsuitable for structural and electronic applications, such as molded carparts and electrical laminates. Such polymerizations are commonlycarried out in reaction injection molding (RIM) processes, in which ametathesis catalyst and a monomer are charged to a heated mold, andpolymerization of the monomer and forming of the polymer into thedesired shape are carried out simultaneously in the mold.

In such RIM processes, it is important that the polymerization reactionoccur rapidly and with as complete incorporation of the charged monomersas possible. It has been found in molding polydicyclopentadiene, forexample, that the presence of unreacted monomers results in a moldedpart having a very unpleasant odor and less than optimum physicalproperties. In commercial RIM processes, it is economically desirablethat the process be carried out in as short a cycle time as possible andat mold temperature at or near room temperature. It is also advantageousto be able to use an impure monomer stream and thus avoid extensivepurification of the monomer prior to polymerization.

One metathesis catalyst system which has been successfully used in RIMprocesses is the combination of a phenol-treated transition metal salt,such as WOCl₄ or WCl₆, and a co-catalyst such as an aluminum or tincompound. In particular, a phenol-substituted tungsten combined with atin hydride has been found highly efficient for monomer incorporationinto the polymer. This catalyst also is highly active in a relativelyimpure dicyclopentadiene feed stream.

The use of the aluminum and tin co-catalysts, however, has certaindrawbacks. Both co-catalysts require special handling because oftoxicity concerns and sensitivity to air and moisture. In addition, tinco-catalysts are quite expensive. It would therefore be desirable toprovide a co-catalyst for the polymerization of cyclic olefins which haslow sensitivity to air and moisture and relatively low toxicity. Itwould also be desirable to replace the costly tin component of thecatalyst without sacrificing catalyst activity.

It is therefore an object of this invention to provide a catalyst andprocess for the polymerization of cyclic olefins. In one embodiment, itis an object of the invention to provide a co-catalyst which hasrelatively low toxicity and is stable in the presence of air andmoisture. In a further embodiment, it is an object of the invention toprovide a reaction injection molding process.

BRIEF DESCRIPTION OF THE INVENTION

According to the invention, a process and catalyst for thepolymerization of cyclic olefins are provided, wherein a cyclic olefinis polymerized in the presence of a catalyst composition comprising (a)a transition metal compound and (b) a borohydride co-catalyst. In aspecific embodiment, the invention process involves the use of anaryloxy-substituted tungsten halide or oxyhalide, a borohydrideco-catalyst and a boron halide promoter for the reaction injectionmolding of dicyclopentadiene. The invention catalyst and process enablethe rapid polymerization of dicyclopentadiene at relatively low moldtemperatures or relatively low levels of the catalyst.

DETAILED DESCRIPTION OF THE INVENTION The Catalyst

The polymerization catalyst includes a transition metal compound. Thetransition metal is preferably, because of the high activity of theresulting catalyst for dicyclopentadiene polymerization, molybdenum ortungsten. The transition metal compound (or starting material therefor)is generally in the form of a salt, including such salts as halides,including oxyhalides. Suitable halides include chloride, bromide andfluoride. The transition metal halide is preferably one in which thehalide is present in a molar amount of at least three atoms per atom oftransition metal. Examples of such transition metal halides includemolybdenum oxytetrachloride, molybdenum oxytrichloride, molybdenumtrioxyhexachloride, molybdenum trioxypentachloride, molybdenumoxytetrafluoride, tungsten hexachloride, tungsten oxytetrachloride, andtungsten oxytetrabromide. The preferred transition metal compounds,because of their high activity for dicyclopentadiene polymerization, aretungsten hexachloride, tungsten oxytetrachloride, molybdenumoxytrichloride, and mixtures thereof. The transition metal compound willgenerally be present in the polymerization reaction mixture in an amountof from about 0.001 to about 0.5, preferably from about 0.002 to about0.2, most preferably from about 0.02 to about 0.1 mole percent, based onmoles of cyclic olefin monomer present.

The transition metal compound preferably includes the reaction productof the above transition metal salt with an alcohol or phenol forsolubilization and enhanced activity of the transition metal salt. Thesolubilizing compound can be, for example, phenol or an aryl- oralkyl-substituted phenol such as o-, m- and p-cresol; 2-, 3- and4-ethylphenol; 2-, 3- and 4-propylphenol; 2-, 3- and 4-isopropylphenol;2-, 3- and 4-butylphenol; 2-, 3- and 4-tertbutylphenol; 2-, 3-and4-phenylphenol; 2,4- and 2,6-diisopropylphenol; 2,4- and2,6-diisobutylphenol; 2,4- and 2,6-di-tertbutylphenol;2,6-di-tertbutyl-4-methylphenol; 2,4- and 2,6-diphenylphenol. The phenolcan be a halophenol such as, for example, 2-, 3- and 4-fluorophenol;2,3-, 2,4-, 2,5-, 2,6-, 3,4- and 3,5-difluorophenol; 2,3,4-, 2,3,5-,2,3,6-, 3,4,5-, 2,4,5- and 2,4,6 -trifluorophenol; 2,3,4,5-, 2,4,5,6-and2,3,5,6-tetrafluorophenol; pentafluorophenol; and the correspondingbromo- and chlorophenols. The phenol can be a haloalkyl-substitutedphenol such as, for example, 3-trifluoromethylphenol,2-trichloromethylphenol, 4-trifluoromethylphenol,2-trifluoromethylphenol, 3-chlorodifluoromethylphenol,3-dichlorofluoromethylphenol and 3-tribromomethylphenol. Suitablealcohols include, for example, ethanol, isopropanol, t-butanol,octadecanol and the like. Mixtures of such alcohols and phenols can alsobe used.

The phenol will generally be present in the catalyst in an amount ofabout 1 to about 3 moles per mole of the transition metal, preferablyfrom about 1.5 to about 2.5 moles. The reaction product, oraryloxy-substituted transition metal compound, can be prepared, forexample, by contacting, under an oxygen-free inert atmosphere, thealcoholic or phenolic compound and the transition metal compound in aninert organic liquid with mild heat and removal of generated hydrogenhalide. Suitable inert organic liquids for the reaction include, forexample, cyclopentane, cyclohexane, benzene, toluene, xylene,chlorobenzene and dichlorobenzene. The inert organic liquid is thenpreferably distilled off under vacuum, and the residue is dissolved indry, degassed cyclic olefin monomer or other suitable solvent.

The Co-Catalyst

The catalyst includes a borohydride co-catalyst, including thosecompounds which can be represented by the formula [Y+][BH_(m) Z_(n) ]⁻in which Y+ represents an organic or organometallic cationic counterion,Z is a substituent group such as alkyl, cyano, halide and the like, m>0and m+n=4. Particularly preferred are borohydrides represented by theformula [R₃ P]₂ [M+]BH₄ ⁻, in which each R is independently selectedfrom C₁₋₂₀, preferably C₂₋₁₂, hydrocarbyl, preferably aryl. Examples ofsuch borohydrides include transition metal-based borohydrides such asbis(triphenylphosphine) copper(I) borohydride and ammonium borohydridessuch as bis(triphenylphosphoranylidene)ammonium borohydride.Effectiveness of the borohydride depends to some extent on itssolubility in the monomer to be polymerized, and difficulty-solubleborohydrides such as sodium triethyl borohydride, sodium borohydride andtetrabutyl ammonium borohydride are in general not active co-catalystsin non-polar cyclic olefins such as dicyclopentadiene. Preferredco-catalysts, because of their activity in dicyclopentadiene, are thoserepresented by the above formula in which m=4, n=0 and Y+ includesaromatic groups such as triarylphosphine, and tetraaryldiphosphine, suchas 1,2-bis(diphenylphosphine)ethane, moieties.

The amount of the co-catalyst present in the catalyst composition willvary depending on the specific components present and the reactionconditions. In general, the borohydride co-catalyst will be present inan amount within the range of about 0.5 to about 20 or more, preferablyabout 1 to about 10, moles per mole of the transition metal compound.

The invention catalyst can optionally include a boron halide promoter,including boron trihalides, boron trihalide complexes andtetrahaloborates. The promoter can be, for example, such boron halidesas boron tribromide, boron trifluoride, boron trifluoride diethyl ethercomplex, boron trifluoride dibutyl ether complex, boron trifluorideethylamine, tetrafluoroboric acid diethyl ether, methyl borondifluoride, phenyl boron dichloride, triphenylmethyl fluoroborate,ammonium tetrafluoroborate, bis(2-ethyl-1-hexyl)ammoniumtetrafluoroborate, boron trichloride dimethylsulfide, boron trifluoridealcohol complexes, and the like. The boron compound will be present inthe polymerization reaction mixture in an amount effective to promotepolymerization of the cyclic olefin monomer, generally from about 0.01to about 10 moles, preferably from about 0.05 to about 2 moles, per moleof transition metal. The optimum level will vary depending upon thecatalyst and the borohydride, and amounts of boron halide above theoptimum may inhibit polymerization. The presently-preferred boronhalides, because of their high activity and stability, are borontrifluoride and its ethyl ether and butyl ether complexes.

Catalyst Preparation

The preferred catalyst composition of the invention includes anaryloxy-substituted tungsten or molybdenum oxychloride catalyst,optionally combined with an aryloxy-substituted tungsten hexachloride ormolybdenum pentachloride, a borohydride co-catalyst, and a borontrifluoride complex promoter. This catalyst has been found to exhibithigh activity in the polymerization of dicyclopentadiene.

The above catalyst composition is preferably prepared by reacting abouttwo moles of a substituted phenol with one mole of tungsten hexachlorideor tungsten oxytetrachloride, or mixture thereof, in dry inert solventsuch as toluene at a temperature within the range of about 25° to about95° C. under oxygen-free argon. Hydrogen chloride by-product is sweptout of the reaction and the toluene is distilled off under vacuum. Thereaction product is conveniently dissolved in dry, degasseddicyclopentadiene or other liquid monomer to be polymerized, to make asolution about 2 to 10 weight percent in bisphenoxy tungsten compound,which can be diluted with additional monomer to achieve the desiredconcentration of catalyst. The borohydride co-catalyst is generallycombined with the transition metal catalyst in the reaction mixture as asolution of the monomer to be polymerized. The boron halide promoter, ifused, is generally combined with the transition metal and/or borohydrideco-catalyst solution.

Polymerization

The polymerization process of the invention involves contacting one ormore cyclic olefin monomers with the transition metal component in thepresence of the borohydride co-catalyst. Suitable cyclic olefin monomersand comonomers include those of the norbornene type which can berepresented by the structural formulas ##STR1## in which each R isselected independently from hydrogen, C₁₋₂₀ alkyl, C₁₋₂₀ alkenyl, aryland, with R groups linked together through carbon atoms, saturated andunsaturated cyclic hydrocarbon groups. Included in such monomers andcomonomers are dicyclopentadiene, norbornene, norbornadiene and5-(2-propenyl)norbornene. Commercial cyclic olefins are available atvarious levels of purity, ranging from about 92 to about 99.9, the upperpurity ranges being the result of distillation and further treatment forremoval of contaminants and olefins which would be co-polymerized underpolymerization conditions. As a general rule, transition metal catalystsemploying an alkyl aluminum compound as co-catalyst require ahigh-purity monomer for acceptable polymerization activity, while theuse of a borohydride co-catalyst permits the use of lower purity,technical-grade (83-95%) dicyclopentadiene monomer. An advantage of theinvention catalyst is that it is very active in relatively impure(90-95%) dicyclopentadiene.

The invention polymerization process is preferably carried out byreaction injection molding (RIM), in which a solution of the catalyst,preferably in the monomer liquid to be polymerized, is injected into amold simultaneously with the monomer, in liquid form, to be polymerized.The catalyst is generally employed in a molar ratio of RIM monomer totransition metal (mole:mole) of from about 200:1 to about 12,000:1,preferably about 500:1 to about 8000:1, most preferably about 1000:1 toabout 5000:1.

In a preferred RIM polymerization technique, a stream of the transitionmetal catalyst component in the monomer to be polymerized and a monomerstream containing the borohydride co-catalyst are combined in the mixinghead of a RIM machine just prior to injection of the combined streaminto a mold. The boron halide promoter, if used, is injected into themixing head with the transition metal stream, with the co-catalyststream, or in a separate monomer solution stream.

The initial mold temperature will generally be within the range of about20° to about 130° C., preferably about 35° to about 100° C. The moldpressure is generally within the range of about 10 to about 50 psi.After injection of the catalyst and monomer into the mold, there is aninterval of time, called the "induction time," before onset of a rapidexotherm from the exothermic polymerization reaction. In a commercialRIM process, this induction time should be sufficiently long to permitfilling of the mold, typically about 2 minutes, preferably less thanthirty seconds. Once the polymerization reaction is initiated,polymerization should occur quite rapidly, usually within about 10seconds to about 1 minute, and is accompanied by a rapid rise intemperature.

Various optional components can be present in the reaction mixtureduring polymerization, including solvents, fillers, anti-oxidants, flameretardants, blowing agents, stabilizers, forming agents, pigments,plasticizers, reinforcing agents and impact modifiers. Particularlypreferred is the addition of from about 1 to about 10 weight percent,based on the weight of the monomer, of an elastomer for impactmodification of the polymer. These components are most convenientlyadded to the reaction as constituents of one or more of the reactionmixture streams, as liquids or as solutions in the monomer.

After the polymerization reaction is complete, the molded object may besubjected to an optional post-cure treatment at a temperature in therange of about 100° to about 300° C. for about 1 to 24, preferably about1 to 2 hours. Such a post-cure treatment can enhance certain polymerproperties, including glass transition temperature.

The Polymer

The invention RIM process prepares a crosslinked dicyclopentadienehomopolymer or copolymer. The presently preferred polydicyclopentadieneproduct is a crosslinked polymer containing at least about 90 percentdicyclopentadiene monomer units. The polymer will typically have aflexural strength of at least about 5000 psi, preferably greater thanabout 6000 psi, and a Tg of at least about 100° C. (DSC at 20° C/min).The polymer is useful in applications such as structural composites, forexample, in the automobile industry, and in electrical applications suchas printed circuit boards.

EXAMPLE 1 Polymerization with Tungsten Catalyst and BorohydrideCo-Catalyst

Certain specific embodiments of the invention are described in whichdicyclopentadiene was polymerized under laboratory-scale reactioninjection molding conditions using a tungsten-based catalyst and aborohydride co-catalyst. The aryloxy-substituted tungsten catalysts usedin the experimental runs were prepared by reacting tungstenoxytetrachloride with two equivalents or a slight excess of2,6-diisopropylphenol or 1 to 2 equivalents of 2,6-diphenylphenol in drytoluene at 25°-90° C. under oxygen-free, dry argon and, after thehydrogen chloride by-product had been swept from the reaction,distilling the toluene under vacuum. The residue was dissolved in dry,degassed dicyclopentadiene (about 93% purity containing up to 7% C₉ andC₁₀ olefins) to make a 5-8 weight percent solution (referred to ascatalyst master solution). Described procedures were carried out in anitrogen dry box or under purified argon atmosphere.

A series of polymerizations of dicyclopentadiene were made using thetungsten oxychloride catalysts and bis(triphenylphosphine)copper(I)borohydride co-catalyst (Aldrich Chemical Company). The conditions andresults of each run are shown in Table I. In each run, a 30-mL driedserum bottle with a stir bar was charged with the indicated amount ofbis(triphenylphosphine)copper(I) borohydride and about 15 g dry,degassed dicyclopentadiene under nitrogen atmosphere. To the stirredmaterial was added (via syringe) the catalyst master solution containingthe tungsten catalyst. The total amount of dicyclopentadiene in each runwas 16 g. The contents of the bottle were stirred for about 30 seconds.The bottle, containing a thermocouple, was then transferred to an oilbath at 90° C. Indicated on Table I are time to onset of substantialpolymerization of the reaction mass, the internal temperature of thereaction mass at onset, maximum exotherm temperature, and time for thepolymerization reaction mass to reach maximum exotherm.

EXAMPLE 2 Polymerization with Bis(Triphenylphosphoranylidene)AmmoniumBorohydride Co-Catalyst

The polymerization of dicyclopentadiene was conducted essentially as inRun 5 of Example 1 using 0.13 g bis(triphenylphosphoranylidene)ammoniumborohydride co-catalyst (Alfa Chemical Company) and boron trifluoridebutyl ether complex promoter. The polymerization mixture did not displayan exotherm, but set to a hard solid after about 20 minutes in the 90°C. bath.

                                      TABLE 1                                     __________________________________________________________________________    Bulk Polymerization of Dicyclopentadiene With (PH.sub.3).sub.2 Cu +           BH.sub.4 -Cocatalyst                                                             Cocatalyst                                                                          Catalyst                                                                           BF.sub.3.sup.a                                                                    BF.sub.3 /W                                                                       Exotherm Onset                                                                            Exotherm Maximum                            Run                                                                              (mmol)                                                                              (mmol)                                                                             (mmol)                                                                            Ratio                                                                             Time (min)                                                                          Temp (°C.)                                                                   Time (min)                                                                          Temp (°C.)                                                                   Δ T                       __________________________________________________________________________    WOC1.sub.2 (2,6-diisopropylphenoxy).sub.2 catalyst                             1 0.236 0.059                                                                              0.088                                                                             1.5 4.3   84    7.3   106    22                              2 0.236 0.059                                                                              0.059                                                                             1.0 NE (some gel)                                            3 0.236 0.059                                                                              0.059                                                                             1.0 NE (some gel)                                            4 0.232 0.059                                                                              0.059 E                                                                           1.0       NR                                                 5 0.232 0.059                                                                              0.029 E                                                                           0.5 2.5   69    3.1   218   149                              6 0.236 0.059                                                                              0.015                                                                             0.25                                                                              5.0   97    5.4   199   102                              7 0.236 0.059                                                                              0.015                                                                             0.25                                                                              6.1   94    7.3   211   117                              8 0.232 0.059                                                                              --  0   11.5  97    14.3  179    82                               9                                                                              0.232 0.059                                                                              --  0   10.1  105   11.3  201    96                             10 0.236 0.059                                                                              --  0   6.3   106   6.9   208   102                             11 0.184 0.059                                                                              0.032                                                                             0.5 NR                                                      12 0.184 0.059                                                                              0.015                                                                             0.25                                                                              NR                                                      13 0.156 0.039                                                                              0.078                                                                             2.0 4.7   91    7.4   110    19                             14 0.156 0.039                                                                              0.078                                                                             2.0 NE (some gel)                                           15 0.156 0.039                                                                              0.032                                                                             0.8 NE (some gel)                                           16 0.156 0.039                                                                              --  0   7.6   91    12.8   96    5                              17 0.078 0.039                                                                              0.078                                                                             2.0 5.8   94    6.8    99    5                              WOC1.sub.x (2,6-diphenylphenoxy).sub.y catalyst                               18 0.364 0.067.sup.b                                                                        0.091 E                                                                           1.3 3.0   89    3.4   225   136                             19 0.232 0.053.sup.c                                                                        0.059 E                                                                           1.1 2.8   91    4.9   211   120                             __________________________________________________________________________     .sup.a E = ethyl ether complex; all others butyl ether complex                .sup.b X = 2, Y = 2                                                           .sup.c X = 3, Y = 1.                                                          NE = no exotherm                                                              NR = no visible reaction                                                 

I claim:
 1. A composition comprising:(a) a transition metal compoundwhich is the product of reacting a tungsten or molybdenum salt and analcohol or a phenol, which phenol may optionally have substituentsselected from the group consisting of aryl, alkyl, halo and haloalkylsubstituents; and (b) from about 0.5 to about 20 moles per mole of thetransition metal compound of a borohydride which can be represented bythe formula (R₃ P)₂ (M⁺)BH₄ ⁻, in which each R is independently selectedfrom C₁₋₂₀ hydrocarbyl and M⁺ is selected from copper and ammonium. 2.The composition of claim 1 in which component (a) is a reaction productof a transition metal salt and a substituted phenol.
 3. The compositionof claim 2 in which the borohydride is present in the composition in anamount within the range of about 1 to about 10 moles per mole of thetransition metal compound.
 4. The composition of claim 1 in which thephenol is selected from the group consisting of phenol, cresol,ethylphenol, propylphenol, isopropylphenol, butylphenol,tert-butylphenol, phenylphenol, 2,4- and 2,6-diisopropylphenol, 2,4 and2,6-diisobutylphenol, 2,6-di-tert-butylphenol, 2,4- and2,6-di-tert-butyl-4-methylphenol, 2,4- and 2,6-diphenylphenol,fluorophenol, difluorophenol, trifluorophenol, tetrafluorophenol,pentafluorophenol, trifluoromethylphenol, trichloromethylphenol,trifluoromethylphenol, chlorodifluoromethylphenol,dichlorofluoromethylphenol and tribromomethylphenol.
 5. The compositionof claim 1 in which the borohydride is selected from the groupconsisting of bis(triphenylphosphine)copper(I) borohydride andbis(triphenylphosphorarylidene)ammonium borohydride.
 6. The compositionof claim 5 in which the transition metal salt comprises at least onecompound selected from the group consisting of tungsten hexachloride,tungsten oxytetrachloride and molybdenum oxytrichloride.
 7. Thecomposition of claim 6 in which the phenol is selected from the groupconsisting of t-butyl phenol, t-octyl phenol, nonyl phenol,2,6-diisopropyl phenol, 2,6-di-tert-butyl-4-methylphenol and2,6-diphenylphenol.
 8. The composition of claim 1 which furthercomprises from about 0.01 to about 10 moles, per mole of the transitionmetal compound, of a boron halide.
 9. The composition of claim 8 whichfurther comprises a cyclic olefin.
 10. The composition of claim 9 inwhich component (a) is a reaction product of a transition metal salt anda phenol selected from the group consisting of 2,6-diisopropyl phenoland 2,6-diphenylphenol.
 11. The composition of claim 8 in which theboron halide is selected from the group consisting of boron tribromide,boron trifluoride ethyl ether complex, boron trifluoride ethylamine andboron trifluoride butyl ether complex.
 12. The composition of claim 9 inwhich the borohydride is bis(triphenylphosphine)copper(I) borohydride.13. The composition of claim 12 in which the transition metal salt is amixture of tungsten hexachloride and tungsten oxytetrachloride.
 14. Thecomposition of claim 13 in which the phenol is selected from halophenolsand haloalkyl-substituted phenols.
 15. The composition of claim 9 inwhich the boron halide is present in the composition in an amount withinthe range of about 0.05 to about 2 moles per mole of the transitionmetal compound.
 16. The composition of claim 15 in which the borohydrideis bis(triphenylphosphine)copper(I) borohydride.